Apparatus and method for coating sheet or strip articles

ABSTRACT

A coating head, and coating apparatus and methods using the coating head, for applying a solvent free coating material to a strip article advancing longitudinally in a coating line. The head includes a die having a transverse slit through which the coating material is deposited on the strip surface and having a land portion with an extended land surface on the exit side of the slit, the die being supported for movement normal to the strip surface, and one or more air or hydraulic cylinders exerting a load on at least the land portion of the die to urge the land surface toward the strip, wherein the die is constituted of a main body and the land portion, and the land portion is so connected to the main die body as to be capable of flexing relative to the main die body in a direction normal to the strip surface but to resist flexing in the direction of strip advance in the coating line.

This application is a national stage application of PCT/CA98/00611,filed Jun. 26, 1998, which application claims the priority benefit ofU.S. provisional patent application Ser. No. 60/051,087, filed Jun. 27,1997.

TECHNICAL FIELD

This invention relates to the continuous coating of sheet or striparticles, such as aluminum or other metal strip, hereinafter genericallytermed “strip articles.” In an important sense, it is directed tocoating heads especially suitable for applying low solvent or reducedsolvent coatings or solvent free coatings, e.g. molten polymers, and tocoating lines and methods employing such heads.

BACKGROUND ART

More particularly, the present invention is directed to improvements inthe types of strip-coating apparatus and methods described in U.S. Pat.No. 4,675,230 and in International (PCT) Application No. PCT/CA94/00291published Dec. 8, 1994, under International Publication No. WO 94/27739.

U.S. Pat. No. 4,675,230 describes apparatus and procedure for applying apaint or like coating to an elongated strip article using a coating headwith a die that has a slit to which coating material is supplied underpressure and a strip-facing extended surface or metering landimmediately downstream of the slit, and a support such as a roll aroundwhich the strip is advanced past the head for receiving from the slit alayer of paint metered between the die and the strip, wherein a load iscontinuously exerted on the die during operation for urging the landagainst the applied paint layer on the strip so as to maintain a uniformmetering gap between the land and the coated strip surface. The load maybe exerted by devices such as air cylinders acting on the die andcapable of adjustment to vary the magnitude of the load for differentcoating operations. In this way, a coating of superior uniformity canreadily be applied to a surface of an article such as sheet metal strip,notwithstanding that the strip characteristically exhibits somevariation in thickness along its length; the maintenance of a load onthe coating head die facilitates accuracy and ease of setup, and alsoenables the die to conform positionally to variations in stripthickness, for maintaining a constant metering orifice aperture. U.S.Pat. No. 5,147,462 describes apparatus for automatic film thicknesscontrol in coating procedures and apparatus of the same general type.

The methods and apparatus of U.S. Pat. No. 4,675,230 are shown asarranged for applying a coating to one major surface of a strip article(one-sided coating). The aforementioned PCT publication describesmodifications or arrangements of methods and apparatus of this typeenabling simultaneous application of coatings to both major surfaces ofa moving strip or sheet (two-sided coating). The apparatus arrangementsthus described for two-sided coating comprise two coating heads of thegeneral type described in U.S. Pat. No. 4,675,320, mounted face-to-facewith the strip passing between them.

In particular, the aforementioned PCT publication discloses apparatusfor continuous two-sided coating of a strip article, including means fordefining a path of continuous longitudinal advance of an elongated striparticle having opposed major surfaces to be coated, the path including arectilinear portion in which the opposed surfaces of the strip articleare substantially planar; two coating heads each including a diedefining an elongated open-sided slit and having a land portion with anextended land surface immediately adjacent the exit side of the slit,for respectively depositing layers. of liquid coating material on theopposed major surfaces of a strip article advancing in the path; andmeans for supplying liquid coating material under pressure to the slitof each head. The apparatus thus disclosed also includes means forsupporting the dies of the two heads in facing relation to each other onopposite sides of the rectilinear portion of the strip article pathwhile permitting individual translational movement of at least the landportion of at least one of the dies relative to the supporting means ina direction perpendicular to the major surfaces of a strip articleadvancing in the path. This supporting means positions the heads suchthat their die slits respectively open toward the opposed major surfacesof an advancing strip article in the rectilinear path portion with theirlong dimensions extending transversely of the path; their die landsurfaces are disposed, substantially in register with each other, beyondthe slits in the direction of strip article advance, respectively facingthe opposed major surfaces of an advancing strip article and convergingtoward each other and toward the path in the direction of articleadvance; and, during operation with the article advancing past the slitsand liquid coating material supplied to both slits as aforesaid, thearticle major surfaces respectively drag layers of coating material fromthe slits, the layers being thereby deposited on the article majorsurfaces. In combination with the foregoing features, the disclosedapparatus further includes means for continuously exerting a load on atleast the land portion of the aforementioned one die during operation asaforesaid such that the layers of coating material deposited on thestrip major surfaces are pressed between the land surfaces of the diesof the heads to maintain the deposited coating layers at predeterminedconstant thicknesses while the coating layers alone hold the diesentirely away from contact with the strip article major surfaces.

In some embodiments of the described apparatus, the aforementioned onedie comprises a land portion as defined above and a portion that isstationary during operation, the land portion being movable relative tothe stationary portion and cooperating therewith to define the slit. Theload-exerting means, in these embodiments, acts between the supportingmeans and the movable land portion of the die. In other embodiments, theaforementioned one die is formed integrally and the load-exerting meansacts between the supporting means and the entire die, which is supportedon a bearing so as to be capable of moving as a unit relative to thesupporting means during operation. The other die (including its landportion) can be held entirely stationary during the coating operation,or, alternatively, the dies of both heads (or their land portions) canbe movable relative to the supporting means during operation and canboth be acted on by load-exerting means.

In the heads of the aforementioned U.S. Pat. No. 4,675,230 and PCTpublication, the load-exerting means for the (or each) die convenientlycomprises at least one air cylinder acting thereon. Preferably, theload-exerting means comprises a plurality of air cylinders acting atpoints spaced along the length of the die, and the die is madesufficiently flexible to conform to variations of strip thickness acrossthe width of the strip, for enhanced coating uniformity.

Heretofore, coating heads for use in the apparatus and methods describedin the aforementioned patents and publication have been designed with arelatively small cross-section so that the complete die (including landportion) of the head could be flexed by modest applied forces. Toachieve the required degree of flexibility for conforming to stripthickness variations as just described, the overall cross-sectionaldimensions of the die should not exceed about four inches (10 cm) andshould preferably be less than two inches (5 cm). Slot dies forsolvent-borne coatings can readily be designed to meet this requirement.However, for solvent free coatings (solvent free molten polymercoatings), the dies must incorporate heating elements and must havespecially designed, polished channels to ensure uniform distribution ofthe coating. For these reasons, typical polymer extrusion dies haveoverall cross-sectional dimensions in excess of six inches (15 cm). Itwould not be possible to control the flexing of a die with thesedimensions, without resorting to very high loading forces.

DISCLOSURE OF THE INVENTION

The present invention, in a first aspect, broadly contemplates theprovision, in apparatus for continuously coating a major surface of astrip article while the article is advancing longitudinally along adefined path, of a coating head including a die defining an elongatedslit, with an entry side and an exit side, for depositing a layer ofliquid coating material on a facing major surface of a strip articleadvancing along the path, and having a land portion with an extendedland surface at the slit exit side; means for supplying liquid coatingmaterial to the slit; means for supporting the die with the slit andland surface facing the path and the slit extending transversely of thepath such that during coating operation a major surface of a striparticle advancing in the path past the slit drags a layer of coatingmaterial from the slit, the supporting means permitting movement of thedie relative thereto in a direction normal to the path and to the slit;and means for continuously exerting a load on at least the land portionof the die during operation as aforesaid such that the layer of coatingmaterial deposited on the last-mentioned article major surface ispressed between the land surface and the last-mentioned article majorsurface to maintain the layer at a predetermined constant thicknesswhile the layer alone holds the die entirely away from contact with thelast-mentioned article major surface; the die including a main bodydefining at least the entry side of the slit, and the land portion beingso connected to the main die body as to be capable of flexing relativethereto in the aforesaid normal direction but to resist flexing in thedirection of article advance in the path.

It will be understood that, when the die is supported as described aboverelative to an advancing strip article, the land portion (at the exitside of the slit) extends transversely of the strip article majorsurface to be coated. In this coating head, the defined connection ofthe land portion to the main body of the coating head die affords thecharacteristic flexing properties of the metering portion of a coatinghead of the type described in U.S. Pat. No. 4,675,230, even though themain body of the die may have the increased bulk and thickness needed toaccommodate built-in heating elements for solvent free molten polymercoatings, and may therefore be incapable of flexing. At the same time,the movability of the entire die in the aforesaid normal directionrelative to the supporting means enables coarse positional adjustment ofthe die, so that the tolerances of the head and support components donot have to be as exact as would be necessary if only the land portionwere movable.

As further particular features of the invention, the land portion isadvantageously formed integrally with the main body of the die, and theload-exerting means exerts the load directly on the land portion. Theland portion can be cantilevered with respect to the main die body, or,in currently preferred embodiments of the invention, the land portioncan be flexibly connected to the main die body on two opposed sides ofthe land portion respectively toward and away from the slit (upstreamand downstream of the land surface, as stated with reference to thedirection of strip advance in the path).

Moreover, in currently preferred embodiments of the coating head of theinvention, the load-exerting means comprises a piston movable in theaforesaid normal direction and means connected to the piston fortransmitting the load directly to the land portion, the last-mentionedmeans being interengageable with the main die body for permitting butlimiting the extent of motion of the piston and land portion relative tothe main body in the aforesaid normal direction. In particular, the landportion may have a second surface opposed to the land surface; thetransmitting means may include a chock attached to the piston, a rod forload-transmitting engagement with the second surface of the landportion, and a lateral projection (such as a pin or dovetail protection)carried by the chock; and the main die body may include a socket (recessor aperture) within which the projection is received, the projection andsocket being positioned and dimensioned to permit a limited extent ofmotion of the projection within the socket in the aforesaid normaldirection. Also, in these embodiments, the transmitting means cantransmit a force from the piston to the main die body for moving(lifting) the die relative to the supporting means in the normaldirection.

The invention in a further aspect contemplates the provision of acoating line for continuously coating a major surface of a strip articlewhile the article is advancing longitudinally along a defined path,comprising the combination of a head as described above with means fordefining a path and direction of continuous longitudinal advance of astrip article having a major surface to be coated. The coating line. maybe arranged to coat one or both major surfaces of a strip article; in aline for coating two opposed surfaces of a strip article, the pathincludes a rectilinear portion in which the opposed surfaces aresubstantially planar, the supporting means supports the above-describedcoating head at that rectilinear portion of said path such that during acoating operation the slit faces one of the opposed major surfaces of astrip article advancing along the path, and a second coating head isdisposed at the rectilinear path portion in opposed relation to thefirst-mentioned coating head, for depositing a layer of liquid coatingmaterial on the other of the opposed major surfaces of the striparticle.

In yet another aspect, the invention contemplates the provision of amethod of continuously applying a layer of liquid coating material to amajor surface of an elongated flexible strip article, utilizing acoating line incorporating the above-described coating head of theinvention. This method, again, may be used to effect coating of one orboth major surfaces of a strip article very advantageously, it can beused to coat one or both major surfaces of a strip article with asolvent free liquid coating material, such as a molten polymer.

Further features and advantages of the invention will be apparent fromthe detailed description hereinbelow set forth, together with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a highly simplified and schematic side elevational sectionalview of a coating head, and associated elements of a two-sided aluminumstrip coating line, embodying the present invention in a particularform;

FIG. 1B is an enlarged fragmentary side elevational sectional view of aportion of the FIG. 1A head;

FIG. 2 is a reduced and further simplified schematic side elevationalsectional view of a complete two-sided aluminum strip coating line inwhich the head and other elements of FIG. 1 may be incorporated;

FIG. 3A is a side elevational sectional view, at a scale intermediateFIG. 1 and FIG. 2, of a currently preferred embodiment of the die of thecoating head of the invention and an associated fixed die (for two-sidedcoating of aluminum strip) in a first vertical plane parallel to thepath of strip advance;

FIG. 3B is a view, similar to FIG. 3A, of the same coating head dies ina second vertical plane parallel to the strip path;

FIG. 4A is a simplified, larger-scale, side elevational sectional viewof the preferred coating head die of FIG. 3A, as seen from the sideopposite that of FIG. 3A;

FIGS. 4B and 4C are views similar to FIG. 1A of a coating headincorporating the die of FIG. 3A, in operative (coating) and inoperative(raised) positions, respectively;

FIGS. 4D and 4E are views similar to FIGS. 4B and 4C, respectively, of amodified form of the coating head and die;

FIG. 5 is a simplified sectional plan view of the coating head die ofFIG. 3A, at a reduced scale;

FIG. 6A is a side elevational sectional view of another embodiment ofthe coating head of the invention;

FIG. 6B is a fragmentary front elevational sectional view of the coatinghead of FIG. 6A;

FIG. 7 is a highly simplified and schematic side elevational sectionalview, similar to FIG. 1, of a further embodiment of the invention;

FIG. 8 is a view similar to FIG. 7 of yet another embodiment of theinvention; and

FIG. 9 is a simplified side elevational sectional view of yet anotherembodiment of the coating line of the invention.

BEST MODES FOR CARRYING OUT THE INVENTION

For purposes of illustration, the invention will be described asembodied in coating heads, lines and methods for continuously andsimultaneously coating both opposed major surfaces of a flexible stripof sheet aluminum metal (the term “aluminum” herein genericallydesignating pure aluminum metal and aluminum-based alloys) with solventfree liquid coating material, viz., molten polymer. In its broaderaspects, however, the invention may be used for a wide range of coatingoperations, substrates, and coating materials, such as for one-sidedcoating, for coating of strip articles other than aluminum strip orsheet (e.g., aluminum foil, sheet or foil of steel or other metals,paper, plastic sheet or films, etc.), and for applying liquid coatingmaterials other than 100% solids coatings (e.g., low solvent or reducedsolvent coatings, or standard coating formulations including lacquersand paints, lubricants, etc.).

In the coating line schematically shown in FIGS. 1A, 1B and 2, a metalstrip article (e.g., sheet aluminum strip) 10 to be coated iscontinuously advanced, in a direction longitudinally parallel to itslong dimension, from a coil 11 along a path (represented by arrows 12)of which at least a portion 14 is rectilinear, in which portion themajor surfaces of the advancing strip are substantially planar.Preferably the path portion 14 is horizontal. At a locality in this pathportion 14, molten polymer is applied to both major surfaces 16, 18 ofthe strip from two coating devices 20 and 22 (disposed in register witheach other respectively above and below the path portion 14 and thusrespectively facing the upper and lower major surfaces of the striparticle) to establish on each of the strip surfaces a continuous layeror coating 17, 19 of the polymer. Since, for molten polymer coating, thestrip must generally be preheated to a temperature close to the meltingpoint of the polymer to be applied, the strip is shown as passingthrough a preheating zone or station 23 (including heat sources, e.g. ofconventional character, not shown, to effect the requisite elevation ofstrip temperature) just ahead of the coating devices 20, 22. Beyond thecoating devices in the path of strip advance, the strip is passedthrough a heating zone 24 to postheat the coating. After postheating,the coated strip is subjected to cooling as with a conventional waterspray quench and/or air jets schematically indicated at a cooling zoneor station 25, and is then coiled again, e.g. on a driven rewind reel 26which constitutes the means for advancing the strip through the coatingline. It will be understood that the arrangement of coil 11 and reel 26,with the associated postheating zone 24, is merely exemplary of meansfor continuously advancing the strip longitudinally along a path havinga horizontal rectilinear portion 14 at which the coating devices 20 and22 are located.

The coating device or coating head 20 includes a rigid coating die 28comprising a metal block having a surface 30 facing and spaced from theupwardly-facing major surface 16 of the advancing strip article todefine therewith a gap 32. The die 28 extends over the entire width ofthe strip at a locality, in the portion 14 of the path of strip advance,at which the strip is also passing over the lower coating device orcoating head 22.

Formed in the die 28 is an elongated slit 34 which opens outwardlythrough the surface 30 of the die. This slit is axially rectilinear andof uniform cross-section throughout, with its ends closed by dams orshutters (not shown) inserted in and positionally adjustable along theslit to define the ends of the effective (polymer-discharging) apertureof the slit. It is oriented with its long dimension extendinghorizontally and perpendicular to the direction of advance of the strip10.

An elongated enclosed manifold chamber 36, typically or preferably of“coat-hanger” configuration, extends within the die 28 along the lengthof the slit, for containing liquid coating material (molten polymer)under pressure. The slit communicates inwardly with this chamber alongthe entire length thereof, so that molten polymer (supplied to themanifold chamber through a feed passage 38 constituted of a successionof insulated and flexible tubes and connectors) flows from the manifoldchamber through the slit. In operation, molten polymer is continuouslydelivered from a source (not shown) under pressure (by any suitable,e.g. conventional, means, not shown) to the manifold chamber at a ratesufficient to keep the manifold chamber entirely filled and to force thepolymer therefrom under pressure through the slit 34, so that the slitas well is continuously entirely filled with molten polymer underpressure.

As will be understood from the foregoing description, the slit 34,opening through surface 30, extends transversely of the path of stripadvance. The location and length of the effective aperture of the slit(established, for example, by the aforementioned dams or shutters)determine the position and width, on the advancing strip, of the coatingto be applied. That is to say, the effective aperture of the slit,through which polymer is delivered to the facing strip surface, has alength less than or equal to the strip width, and is disposed forregister with that portion of the width of the strip surface 16 which isto be coated. Stated with reference to the direction of advance of thestrip past the die 28, the upstream edge of the slit opening issometimes referred to herein as the entry side, and the downstream edgeof the slit opening is sometimes referred to as the exit side of theslit.

The described arrangement of slit and strip results in deposit ofpolymer from the slit onto the strip surface 16 over the full width ofthe portion of the surface 16 that coincides with the effective apertureof the slit, i.e. when the slit is filled with molten polymer deliveredthrough manifold chamber 36. The deposited polymer is carried out of theslit as a coating on the advancing strip surface 16, past the exit sideof the slit and through the gap between the surface 30 and the stripsurface 16 beyond the slit. The downstream edge 42 of surface 30, formedas a sharp discontinuity between the surface 30 and a downstreamfacing,generally vertical surface portion 44, extends across the width of thedeposited polymer coating on the strip surface 16 and, together with thesurface 16, defines a metering orifice that determines the thickness ofpolymer coating carried on the strip away from the die; as will beunderstood, the spacing between the surface 16 and edge 42 should besuch as to constitute a gap providing a desired wet thickness of polymercoating on the surface 16, this wet thickness being less than theaperture of the gap. The coated strip surface emerges from beneath thedie past edge 42. Preferably, the surface portion 44 meets surface 30 atan angle (at edge 42) of not more than about 90°, for assured avoidanceof pick-up of polymer from the strip onto the surface portion 44.

The slit 34 and edge 42 of the die 28 are spaced apart, in the directionof strip advance, so that an extended portion 30 a of the surface 30lies between them. Provision of this extended surface portion 30 a(hereinafter referred to as a land surface), facing the strip surface 16downstream of slit 34, is important for the coating operation of theinvention. The land surface 30 a is oriented to progressively approachthe facing strip surface 16 in the direction of strip advance such thatsurfaces 30 a and 16 converge in the latter direction, with the distancebetween strip and head reaching a minimum at edge 42.

As shown, the upstream and downstream lips of the slit 34, including thedownstream lip bearing the land surface 30 a and edge 42, may beprovided as replaceable inserts 45 a, 45 b suitably mounted to the diebody.

The head 20 further includes structure 46 for supporting the die 28 forvertical movement toward and away from the upwardly facing major surface16 of a strip advancing in the horizontal path portion 14, i.e., formovement in a direction normal to the path and also normal to thehorizontal slit 34 which extends transversely of the path. The tubes ofthe feed passage 38 are carried by the support structure and communicatewith a central locality of the manifold chamber of the die through aconnector suitably designed to accommodate limited vertical movement ofthe die relative to the stationary support structure. It will beunderstood that while the support structure 46 is typically fixed inposition during a coating operation, it may itself be pivotally mountedso that the entire coating head 20 can be adjusted in angle and/or swungclear of the strip path.

In addition, the coating head 20 includes means acting between thesupport structure 46 and the die 28 (and in particular against a portionof the die which bears land surface 30 a) for continuously exerting aload on the die (and on the latter portion thereof) to urge the landsurface 30 a toward the facing major surface 16 of the strip 10. Thisload-exerting means, in the illustrated embodiment of the apparatus,comprises a plurality of air cylinders (one being shown at 48) fixedlysecured to the support structure 46 above the die 28. Each air cylinderincludes a piston having a shaft 50 which extends downwardly from thecylinder to bear against an upwardly facing surface of the die 28 or aportion thereof.

Thus, actuation of the air cylinders (which may be of a generallyconventional character and accordingly need not be described in detail)causes the piston shafts 50 to push the die 28 toward the surface 16 ofstrip 10 advancing in path portion 14. Advantageously, the localities ofengagement of the air cylinder piston shafts with the die are arrangedto act on the die at locations spaced along the slit long dimension.

Alternatively, in other embodiments of the invention, the load-exertingmeans may comprise a single air cylinder, or one or a plurality ofhydraulic cylinders, or other devices (such as one or a plurality ofhelical springs under compression between the supporting structure andthe die) capable of yieldably exerting a load on the die to urge theland surface toward the facing, advancing strip major surface.

The lower coating head 22 includes a die 52 which (like the upper headdie 28) has a horizontally elongated slit 54 extending transversely ofthe path of strip advance and opening, through a surface 56 of the die52, toward a facing major surface of the strip 10, in this case thedownwardly facing strip major surface 18. The portion of surface 56immediately downstream of the outlet edge or exit side of slit 54constitutes a land surface 56 a (similar to land surface 30 a of theupper head die), converging in a downstream direction toward the stripsurface 18 and terminating in a sharp transverse downstream edge 58corresponding to the edge 42 of the upper head die. Molten polymer issupplied under pressure to the slit 54, along the length thereof, so asto be dragged from the slit as a layer on the strip surface 18, thelayer being metered at the metering orifice defined between the latterstrip surface and the edge 58. The lower head die 52, however, isstationary and fixed in position, rather than being vertically movableduring coating operation. The upper and lower slits (34 and 54,respectively) are positioned in register with each other.

In this apparatus arrangement, then, there are provided two coating headdies 28, 52, each defining an elongated open-sided slit (34, 54) andhaving a land surface (30 a, 56 a) immediately adjacent the exit side ofthe slit, for respectively depositing layers of liquid coating material(molten polymer) on the opposed major surfaces 16 and 18 of a striparticle 10 advancing in the path 12; and means for supplying the moltenpolymer under pressure to the slit of each die.

The movable support of the upper head die 28 permits variation in thevertical spacing between the land surfaces 30 a and 56 a notwithstandingthat the lower head die 52 is stationary. The heads 20 and 22 are sopositioned that their slits respectively open toward the opposed majorsurfaces of an advancing strip article in the rectilinear path portion14 with the long dimensions of the slits extending transversely of thepath, and with the respective land surfaces of the two dies disposed,substantially in register with each other, beyond the slits in thedirection of strip article advance. These extended surfaces respectivelyface the opposed major strip surfaces 16 and 18 and converge toward eachother and toward the strip surfaces in the direction of article advance.During operation, with the strip article advancing past the slits andmolten polymer supplied to both slits, the article major surfacesrespectively drag layers of coating material from the slits, the layersbeing thereby deposited on the article major surfaces.

The air cylinders constitute means for continuously exerting a load onthe upper head die and, in particular, the portion thereof bearing theland surface 30 a, to urge the latter surface downwardly, toward theupwardly-facing major surface of a strip article advancing in the pathportion 14, and of course also toward the land surface 56 a of the lowerhead die, this load acting on the strip through the coating layer onsurface 16 such that, during operation as aforesaid, both land surfacesare effectively urged by the load-exerting means against the respectivelayers of coating material deposited on the strip major surfaces tomaintain the deposited coating layers at predetermined constantthicknesses while the coating layers alone hold the heads entirely awayfrom contact with the strip article major surfaces.

At all times, contact between the moving strip and the diesurfaces/edges is prevented. In an illustrative startup procedure, thetwo dies are positioned close to, but not in contact with, the slowlymoving strip; flow of polymer to the dies is started so that a bead ofpolymer develops at the exit slot of each die; the dies are broughttogether with a minimum applied pressure, the strip is accelerated to apredetermined coating speed, and the desired pressure is applied to thecylinders. Thereby, a metering orifice is defined between each head edge42 or 58 and the facing strip surface 16 or 18, the size (aperture) ofthis orifice being determined (for molten polymers of a given viscosity)by the magnitude of the load exerted on the die 28 by the cylinders 48.

The rates of polymer flow through the slits, and the fluid pressure ofpolymer acting on the strip surfaces in the gaps beyond the slits, areprimarily determined by drag forces of the strip rather than by thesupply pressure of polymer in the coating heads. Thus, a small positivepolymer supply pressure is typically sufficient, and the aforementioneddrag forces, as the strip surface moves past the slot opening, createmuch higher fluid pressures between the strip surfaces and the facingland surfaces.

As advance of the strip 10 continues, with continuing supply of polymerunder pressure to the slits, uniform layers of polymer are deposited onthe opposed strip surfaces. Throughout the operation, the cylinderscontinuously maintain a load on the die 28, effectively urging both diestoward the strip surfaces being coated, and these loads serve tomaintain the apertures of the aforementioned metering orifices constant,regardless of local variations in strip thickness. In effect,.each landsurface 30 a or 56 a floats on the layer of polymer being appliedthrough its associated slit 34 or 54, and is maintained (by that layeralone) entirely away from contact with the facing strip surface whilecoating proceeds. The invariant aperture of each metering orifice,resulting from the described load, produces polymer coatings of uniformthickness.

Stated more generally, the purpose of the load-exerting means is toexert, on the applied liquid coating layer between each coating head andthe facing strip surface, a load which is maintained essentiallyconstant across the full width of the strip and throughout the durationof a given coating operation, thereby to achieve the desired constantand uniform aperture of the metering orifice.

Satisfactory operation of the described coating line requires that theclearances between the land surfaces 30 a and 56 a of both dies and thestrip converge in the direction of sheet travel, to generate ahydrodynamic pressure, between the extended surface of each head and thestrip, that will increase as the strip gets closer to the land surface.Provided that the angles of convergence ate chosen correctly, there willbe an equilibrium position for the strip where the pressure forces onboth sides will be equal.

The coating line tends to be self-centering in operation, in that thegreater the force that is applied by the air cylinders 48 to the upperhead die 28, the more counteracting force pushes up on the lower surfaceof the strip. The position of equilibrium and hence the coating filmthickness distribution on the two major surfaces of the strip can becontrolled in two ways, viz. by varying either the angle of convergenceor the lengths (in the direction of strip advance) of the extendedsurfaces of the heads. Within limits, increasing the angle ofconvergence will increase the hydrodynamic pressures generated.Therefore, increasing the angle for one of the two heads will cause theposition of strip equilibrium to shift away from that head and thecoating film thickness on that side of the strip will increase (suitablemeans for adjusting this angle may be provided as shown in U.S. Pat. No.4,675,230 and the aforementioned PCT publication. Similarly, increasingthe length of the extended surface of one of the heads will cause thefilm thickness to increase on that side of the strip.

As thus far described, the coating line of FIGS. 1A, 1B and 2 isgenerally similar to those of the aforementioned U.S. Pat. No. 4,675,230and especially certain two-sided coating lines of the aforementioned PCTpublication. Like those coating lines, the coating line of the presentinvention in the described embodiment incorporates a die for applyingand controlling the distribution and thickness of a coating medium ontoa moving sheet metal surface or other suitable substrate.

As a particular feature of the present invention, however, the design(now to be described) of the upper head die 28 is such that a die lip orland portion 60 on the exit side of the die 28 can be flexed in adirection which is normal to the major surfaces of the strip advancingin the path portion 14 to be coated, but resists flexing in thedirection parallel to the strip major surfaces. Furthermore, by choosingthe particular die materials and cross-section dimensions in the portion60, the flexibility can be engineered to meet the process requirements.

In the embodiment of FIGS. 1A and 1B, the land portion 60 bears the landsurface 30 a as well as the downstream edge 42 and vertical surface 44,and defines the downstream side of the slit 34 along the full length ofthe slit. The main body 28 a of the die 28 (including the portiondefining the upstream side of the slit, and the manifold chamber) is ofsuch cross-sectional dimensions as to be substantially rigid withinsignificant deflections arising from the internal pressure of thecoating material and the various forces which act upon it. The landportion 30 a, in this embodiment, is formed integrally with the main diebody 28 a and is cantilevered relative thereto, with a free lower orouter end bearing the land surface 30 a on the exit side of slit 34,being dimensioned and designed so that it can flex to accommodatevariations in gauge and flatness of the strip 10 being coated (as shown,the cross-sectional dimension of the portion 60 in the plane of FIG. 1Ais relatively narrow for most of its length). The flexing of the die lipor land portion 60 occurs in response to the combination of hydrodynamicpressure generated under the die lip and due to the liquid coating whichis being applied, and the forces applied by the pneumatic or hydrauliccylinders 48. The cross-sectional dimensions of this cantilevered upperdie land portion are such that it is flexible enough to accommodatevariations on the order of 150 microns over the width of the die. Itshould be noted that the stiffness of the section will not allow theland portion 60 of the die to conform to short wavelength stripvariations of less than a few centimeters across the width but willallow it to respond to longer range variations. This gives a “smoothing”effect as the coating is applied.

Forces act on the die land/lip portion 60 in the direction of stripadvance in the path 12 owing to viscous drag by the coating, and to thepolymer pressure in the slit. These forces tend to deflect the die landportion 60 in a direction parallel to the direction of strip advance.Since this can be undesirable, the shape and dimensions of the die andits cantilevered land portion are selected so that the land portion willbe relatively resistant to bending or flexing in the strip-advancingdirection.

Since the main die body 28 a and the flexible land portion 60respectively define opposite (upstream and downstream) sides of the slit34 and its associated feed channel for flow of polymer, deflection(flexing) of the land portion relative to the main die body will cause achange in the dimension of the channel through which the polymer flows.In turn, this will affect the flow rate of the coating. However, for theintended applications (coating sheet materials), the amount of suchvariation in channel dimension (a few microns), in a total channel widthof 1 mm or more, will not have a noticeable effect.

As already mentioned, for application of 100% solids coating materials(molten polymers), the dies of the coating line must incorporate heatingelements and must have specially designed, polished channels to ensureuniform distribution of the coating. These elements and channels can beaccommodated in the main die body 28 a of the embodiment of FIGS. 1A and1B. At the same time, by the provision of a lip or land portion 60 whichis flexible enough to conform to the sheet, the invention overcomes theproblem of achieving requisite flexibility in a die that must have suchheating elements and special channels. That is to say, in the coatinghead die of the invention, the part of the die which needs to beflexible is flexible, and the main body of the die is substantiallyrobust and stiff.

It may be noted that the flexible land portion of the die of the presentinvention differs in significant respects from the variable geometrypolymer film extrusion dies which are commonly used in the plasticsindustry, e.g. as described in U.S. Pat. No. 5,067,432, issued Nov. 26,1991. The latter dies have an adjustable lip designed to allow the slotdimension of the die to be changed so that the polymer flow and filmthickness across the width of the die can be adjusted (usually to getuniform thickness in extruded film); in the dies of the presentinvention, the purpose of the flexible section is to allow the die lipto maintain a hydrodynamically controlled contact with the coating onthe substrate. Any incidental changes in the slot width will be verysmall relative to the total slot width (typically on the order of about1%).

Moreover, in the aforementioned plastic film extrusion dies, the lipadjustment is typically made using a series of set screws and after thisadjustment, the die lip is not free to flex; i.e., the die lip is presetand is not intended to change dynamically during the extrusion of film.In contrast, the dies of the present invention are not preadjusted tofixed positions, but are able to flex in response to the hydrodynamicforces from the coating and to the variable applied pressures from theloading cylinders.

Furthermore, the present design enables the die lip to be displaced in adirection which is normal to the coated surface, while substantiallyresisting displacement in a direction parallel to the coating surface(along the direction of coating).

To summarize, in the embodiment of FIGS. 1A and 1B, the coating head dieof the invention includes, in an integral die block, a main die bodythat is substantially rigid and a cantilevered downstream lip or landportion that can undergo transverse flexing in a direction normal to thesurface of the strip being coated, but not in a direction parallel tothe strip surface. By isolating the movement of the land surface 30 a inthis way, the invention achieves the flexing properties desired for themetering portion of the die even though the main die body must bedimensioned to accommodate heating elements for molten polymer, sincethe heaters can be located in the part of the die not directly involvedwith metering the coating fluid onto the strip surface.

In itself, the flexible lip or land portion of the die can achieve onlya very small amount of vertical flexing movement. To provide a coarseadjustment feature with an advantageously larger range of verticalmovement, the coating head 20 of FIG. 1A includes an arrangement of thedie 28 and support structure 46 enabling the entire die body to move asignificant distance (for example 1 cm. or more) in a directionperpendicular to the surface of the strip being coated. Thus, therelatively massive main die body 28 a, which extends above anddownstream (with respect to the direction of strip travel) as well asupstream of the cantilevered land portion 60, is received within arecess 62 formed within the fixed support structure 46, this recessbeing dimensioned to permit substantial though limited movement of theentire die 28 relative to the support structure. It will be understoodthat the die and recess 62 both extend from end to end of the coatinghead, transversely of the strip being coated, and are substantiallyuniform in dimension and configuration throughout their length.

Within the recess 62, on both the upstream and downstream sides of themain die body 28 a, are provided needle bearing cartridges 64 and 66disposed between the sides of the recess and the die body; the upstreamone of these cartridges is itself horizontally slidable relative to thesupport structure, and is spaced from the adjacent side wall of therecess 62 by Belleville washers 68 that accommodate differentialexpansion of the die and support structure. The needle bearings allowthe die body to slide vertically within the support structure inresponse to the applied forces from the piston rods 50.

The molten polymer inlet passage 38 is represented, in FIG. 1A, asincluding an insulated tube 38 a extending through a clearance hole in atrunnion of the support structure; a flexible tube connector 38 bleading from tube 38 a; and a connector 38 c leading from tube connector38 b to the interior of the die 28. This arrangement is exemplary ofsuitable passage systems for delivering molten polymer to a die that isvertically moveable, as on the illustrated needle bearings, relative tothe support structure of the coating head.

As further shown in FIG. 1A, the air cylinders 48 are mounted above aportion 46 a of the support structure which is above the downstream partof the die body 28 a, and the cylinder pistons 50 extend downwardlythrough Graphalloy bushings 70 inserted in openended passages 72 formedin support structure portion 46 a. For each cylinder and its associatedpiston, there is provided a chock 74 at the lower end of passage 72; thechock is removably secured to the piston by means of a pin 76 so as tomove vertically therewith. The lower end of the chock has a lateralprojection in the form of a dovetail projection 78 which is inserted inan upwardly-opening dovetail socket or recess 80 formed in thedownstream part of the main die body 28 a directly above the landportion 60, the projection 78 and recess 80 being mutually dimensionedto permit limited vertical movement of the chock relative to the diebody. The dovetail feature allows dies to be interchanged quickly andeasily.

Below the dovetail projection of each chock, a push rod 82 extendsdownwardly, through a passage (not shown) in the downstream part of themain die body 28 a, to a flat horizontal upper surface 60 a of the outer(unsupported) end of the cantilevered land portion 60 of the die, suchthat the chock can bear downwardly against the upper end of the pushrod. Through the chock and this push rod, the load exerted by each aircylinder 48 is transmitted directly to the land portion.

While the extent of permitted vertical movement (i.e., in a directionnormal to path 12 and strip 34) of the die 28 as a whole relative to thesupport structure 46 is determined by the relative vertical dimensionsof recess 62 and the portion of die body 28 a received wherein, theextent of permitted vertical movement of the land surface 30 a relativeto the main die body 28 a is determined by the vertical clearancebetween the dovetail projection 78 and dovetail recess 80. Typically,and preferably, there is a relatively large amount of vertical clearancebetween the complete movable die and the rigid supporting structure,compared to a relatively small amount of clearance between the dovetailprojection and dovetail recess.

In the head of FIG. 1A, the dovetail feature is present to enable thedie 28 to be raised (within the vertical clearance provided by recess62) during interruptions in the coating process so that the head can beswung out of the way (the head pivots on the support structure in thedirection of strip movement in order to facilitate servicing). Thecoarse adjustment feature provided by bearings 64 and 66 is presentprimarily for the purpose of aligning the die 28 with the strip 10 atthe start of the coating process so that the die can position itself tofollow the strip profile (i.e. gross surface contour across the width ofthe strip, within which accumulated variation due to machiningtolerances, thermal distortion of the die and sheet gage variation maytotal up to 150μ) and also to compensate for different stripthicknesses. During coating operation, the head is not expected to movemore than about 2μ, which vertical movement is entirely accommodated bythe clearance between dovetail portion 78 and recess 80; this is so, inthe described head, because the force of the air cylinders is applieddirectly to the land via chock 74 bearing on push rod 82 which in turnbears on the land. Of course, if unusually large variations in stripprofile are encountered during a coating run, the coarse adjustmentfeature will automatically be brought into play to result in greatervertical movement of the die.

With this system, the die as a whole will easily adjust in verticalposition to accommodate different sheet gauges, while the flexible lipor land portion 60 can respond quickly to small fluctuations in gaugeboth along and across the strip. That is to say, since the die as awhole is mounted in the needle bearings and acted on by the aircylinders, the land surface 30 a automatically aligns itself with thefacing (upper) major surface 16 of a strip article 10 being coated(coarse adjustment); once the head as a whole is so aligned, the flexingof the land portion 60 takes over to adjust for the small strip surfaceirregularities that could affect the consistency of coatings which areon the order of only a few microns thick (fine adjustment). In this way,the tolerances of the coating head die and support components are lessexact than would be required if only the land portion was movable.

Performance of a strip-coating operation with the coating line of FIGS.1A, 1B and 2 may be generally as described in the aforementioned PCTpublication except that the loading force is exerted on the land surfaceof the movable coating die, and transmitted to the main die body throughthe flexible land portion, which is capable of movement isolated fromthe die as a whole, to enable desired flexing of the landsurface-bearing portion in a die which must be made relatively bulky andrigid to accommodate heating elements for molten polymer coatings.

FIGS. 3A, 3E, 4A, 4B, 4C and 5 illustrate a currently preferred coatinghead die 128, in accordance with the present invention, that may be usedin the coating head 20 of FIG. 1A, i.e., in place of the head 28 withits free-ended cantilevered lip or land portion 60. The die 128 has adownwardly-facing surface 130 through which opens a slit 134 fordischarging liquid coating material (e.g. molten polymer) onto theupwardly-facing major surface of a strip article advancinglongitudinally in the path indicated by arrow 12. The interior of thedie body defines a manifold chamber 138, typically of “coat-hanger”shape, extending along the length of the slit for delivering moltenpolymer thereto. As in the case of the die 28, the die 128 is mountedfor use with its surface 130 and slit 134 facing downwardly andextending horizontally, transversely of the strip surface to be coated.

Spaced downstream from the exit side of the slit is a downstream edge142 of the surface 130, corresponding in position, configuration andfunction to the edge 42 in die 28 of FIGS. 1A and 1B. The extendedportion 130 a of surface 130 between the exit side of the slit and edge142 constitutes a land surface, corresponding to the land surface 30 aof die 28, and converging toward the surface of the strip to be coatedin the direction of strip advance. This land surface 130 a is formed ona relatively flexible lip or land portion 160 of the die 128. The landportion 160 is formed integrally with the main body 128 a of the die anddefines the downstream side of the slit 134, being connected on itsupstream side (with reference to the direction of strip advance) to themain die body by an extended portion 160 a of relatively narrowcross-section, and also being connected on its downstream side to themain die body by a relatively thin web 160 b of the die body material.Thus, the land portion 160, unlike the land portion 60 of FIG. 1A, issupported on both its upstream and downstream sides. Nevertheless, theshapes and cross-sectional dimensions of both the upstream anddownstream connecting portions (160 a and 160 b) are such that the landportion 160 is capable of flexing, relative to the main die body 128 a,in a direction normal to the strip surfaces to be coated, but not in adirection parallel to the strip surfaces; i.e., the same isolation andindependent flexibility of the land portion is thereby provided, for thesame purpose, as in the die 28 of FIG. 1A.

The main die body 128 a in FIGS. 3A-5 is provided, in its upperdownstream portion, with an upwardly opening dovetail socket or recess180 identical to the dovetail recess 80 of the die body in FIG. 1A. Thedie 128 may accordingly be mounted in the recess 62 of the supportingstructure 46 of FIG. 1A, in place of the die 28, and as thus mountedwill function in the same manner as the die 28, with coarse and fineadjustment achieved as described above. As illustrated in FIGS. 4B and4C, when the die 128 of FIGS. 3A-5 is assembled with the supportingstructure and air cylinders of FIG. 1A, the push rod 82 associated witheach piston 50 extends downwardly through an opening 182 a in the maindie body 128 a below the dovetail recess to bear against anupwardly-facing surface of the land portion 160, as represented by arrow182 in FIG. 4A.

More particularly, the pin 76 extends through a forked projection 74 apermanently attached to the lower end of the piston rod 50 and throughthe upper portion 74 b of the chock bearing dovetail projection 78, tosecure the chock to the piston. In coating position (FIG. 4B), with thepiston extended downwardly, the dovetail portion bears against the upperend of push rod 82 to exert force on the die land portion 160. Inretracted position (FIG. 4C), to enable the coating head to be pivotedaway from the strip for servicing, the piston is raised, and thedovetail portion 78 engages the converging upper walls of recess 180 tolift the die 128 upwardly; the dovetail portion is then spaced above thepush rod. It will be appreciated that the illustrated combination ofpiston, chock and push rod is typically one of a plurality of pistons,with associated chocks and push rods, provided at spaced locations alongthe length of the die 128 and transversely of the direction of stripadvance.

In the modification shown in FIGS. 4D and 4E (which again respectivelyshow the coating position and retracted position of the die), the chockincluding dovetail portion 78 is replaced by a chock having a straightportion 78′ extending down from the upper portion 74 b and carrying alateral projection in the form of a horizontal pin 78″ that extendsthrough sockets or apertures of ears 180′ formed on the top of the die128′. The ear apertures are so positioned and dimensioned that, when thepiston is extended downwardly, the chock bears against the push rod 82to exert force on the die land portion 160, and there is clearancebetween pin 78″ and the ears 180′ (similar to that between dovetailportion 78 and recess 180 in FIG. 4B) to permit vertical movement of theland portion relative to the main die body. When the piston is raised,elevating the chock away from the push rod, the pin 78″ engages the ears180′ to lift the die 128′.

FIGS. 3A and 3B, representing sections at different points along thelength of the die 128, illustrate also the arrangement of heatingelements 184 within the main body of the die to keep the polymer moltenduring the coating operation. In addition, FIGS. 3A and 3B show sectionsthrough a preferred form of stationary lower die 152 (corresponding instructure and function to the die 52 of FIG. 1A), again includingheating elements 186 for keeping the polymer molten. It will be seenthat in the die 128 the heating elements can be positioned as close tothe manifold chamber and slit as needed without encroaching upon, oraffecting the bulk and flexibility of, the flexible land portion 160.

FIG. 5, a section through the plane of the slit and coat-hanger cavityof die 128, shows the positional relation of the long dimension of thedie and the width W of the strip being coated.

A modified embodiment of the die of the coating head of the presentinvention is shown in FIGS. 6A and 6B, in side and fragmentary frontelevational sectional views. In this embodiment, the upper head die 228includes a main die body 228 a defining the upstream side of a slit 234with a manifold chamber 238, and a land portion 260 defining thedownstream side of slit 234 and bearing the land surface 230 a whichcorresponds positionally, structurally and functionally to the landsurfaces 30 a of FIGS. 1A and B and 130 a of FIGS. 3A-5. The landportion 260, like that of FIGS. 3A-5, is supported on both its upstreamand downstream sides and is acted on by the pistons 250 of air cylinders248 spaced along the length of the die (FIG. 6B).

FIGS. 7 and 8 show two further embodiments of the coating line and dieof the invention. Each of these embodiments is shown as associated withthe stationary lower coating head 22 of FIG. 1A. In FIG. 7, the upperhead die 328 includes a lower portion 328 a defining the upstream sideof the die slit 334, and an upper portion 360 defining the downstreamside of the slit and carrying the land surface 330 a which correspondsto land surface 30 a of FIG. 1A. While die portion 328 a issubstantially rigid with insignificant deflections arising from theinternal pressure of the coating material and the various forces whichact upon it, die portion 360 is designed (with reduced-thickness region360 a) so that it can flex vertically (in a direction normal to thesurface of a strip article 10 being coated) to accommodate variations ofa few microns in the gauge and flatness of the sheet being coated, butdoes not flex in a direction parallel to the strip surface. Aircylinders or other load-exerting means as discussed above act directlyon the die portion 360, as indicated by arrow 350. The entire die bodyconstituted of portions 328 a and 360 is supported on one side by abearing, such as a needle bearing diagrammatically indicated at 364, soas to be vertically movable (i.e., in a direction normal to the surfaceof the strip article 10 being coated), with an extent of verticalmovement greater than the extent to which the die portion 360 can flexvertically relative to the die portion 328 a.

Similarly, the die 428 of FIG. 8 is provided with a portion capable of aminor degree of flexing in a direction normal to (but not parallel to)the surface of strip article 10 being coated, such portion being actedon by air cylinders (arrow 450); the die is also supported by a needlebearing structure 464 or the like so as to be movable as a whole in theaforesaid normal direction.

Yet another embodiment of the coating head of the invention isillustrated in FIG. 9. In this embodiment, the die 528 has a main diebody 528 a, a lower surface 530, a slit 534, and a land surface 530 a onthe exit side of the slit with a sharp downstream edge 542. The landsurface is carried on a land portion 560 formed integrally with the maindie body and constituting the exit side lip of the slit. Portion 560 hasa thinned, flexible section 560 a, allowing the lip to cantilever, whilethe region 560 b nearer the lip is stiffer providing the smoothingeffect and minimizing flexing parallel to the coating direction. Aircylinders exert a load directly on the lip at region 560 b, as indicatedby arrow 550. The die 528 is carried on fixed support structure by meansof a bearing (not shown) permitting vertical movement of the entire diebody, as in the case of the embodiments of FIGS. 7 and 8.

Although the die 528 can be employed for either one-sided or two-sidedcoating of strip, it is shown in FIG. 9 in a one-sided coating line. Inplace of a lower coating head, the one-sided coating line includesmeans, such as a roll 562 around which the strip 10 is trained, forsupporting the strip on the lower side thereof. The roll 562 (whichrotates in the direction indicated by arrow 564, with the stripadvancing in the direction of arrow 12′) has an axis parallel to thelong dimension of the slit 534 and fixed in relation to the meanssupporting the coating head above the strip. The cylindrical surface ofthe roll is positioned closely adjacent (and beneath) the slit openside; land surface 530 a is shaped and positioned to approachprogressively nearer the roll surface in the direction 12′ of advance ofthe strip.

What is claimed is:
 1. A method of continuously applying a layer ofliquid coating material to a major surface of an elongated flexiblestrip article (10), including continuously longitudinally advancing anelongated flexible strip article (10) having a major surface to becoated along a path, supplying liquid coating material to an elongated,open-sided slit (34) with an entry side and an exit side defined in adie (28) of a coating head, said die including a land portion (60) atthe exit side of the slit (34); characterized by: (a) providing anextended land surface (30 a) at the exit side of slit (34); (b)supporting the die (28) in facing relation to a major surface of a striparticle (10) advancing in the path while permitting individualtranslational movement of the die (28) in a direction normal to thelast-mentioned strip (10) major surface, said die (28) being positionedsuch that the slit (34) opens toward and extends transversely of thelast-mentioned strip (10) major surface, such that said land surface (30a) is disposed facing the last-mentioned major surface of the advancingstrip article (10) and converging toward the path in the direction ofstrip article advance, and such that the last-mentioned article (10)major surface drags a layer of coating material from the slit (34), thelayer being thereby deposited on the last-mentioned article (10) majorsurface; (c) continuously exerting a load on at least said land portion(60) of said die (28) such that the layer of coating material depositedon said last-mentioned article (10) major surface is pressed betweensaid land surface (30 a) and said last-mentioned article (10) majorsurface to maintain said layer at a predetermined constant thicknesswhile said layer alone holds the head (20) entirely away from contactwith the article (10) major surface; (d) said die (28) including a mainbody defining at least the entry side of the slit (34), and said landportion (60) being so connected to said main body as to flex relativethereto in said normal direction as variations in an advancing striparticle (10) pass the land surface, but to resist flexing in thedirection of article advance in said path; (e) said land portion beingformed integrally with said main body; and (f) said load-exerting meansexerting said load directly on the land portion.
 2. A method accordingto claim 1, characterized in that said liquid coating material is asolvent-free coating material.
 3. A method according to claim 2,characterized in that said solvent-free coating material is a moltenpolymer.
 4. A coating head for continuously coating a major surface of astrip article (10) while the article is advancing longitudinally along adefined path, said coating head (20) having a die (28) defining anelongated slit (34), with an entry side and an exit side, for depositinga layer of liquid coating material on a facing major surface of a striparticle (10) advancing along the path, a land portion (60) at the slitexit side and means for supplying liquid coating material to the slit(34); said coating head being characterized by: (a) said land portion(60) having an extended land surface (30 a) at the exit side of slit(34); (b) means for supporting the die (28) with the slit (34) and landsurface (30 a) facing the path and the slit (34) extending transverselyof the path such that during a coating operation a major surface of astrip article (10) advancing in the path past the slit (34) drags alayer of coating material from the slit, said supporting meanspermitting movement of the die (28) relative thereto in a directionnormal to the path and to the slit (34); (c) means for continuouslyexerting a load on at least the land portion (60) of the die duringoperation as aforesaid such that the layer of coating material depositedon the last-mentioned article (10) major surface is pressed between theland surface (30 a) and the last-mentioned article (10) major surface tomaintain the layer at a predetermined constant thickness while the layeralone holds the die (28) entirely away from contact with thelast-mentioned article (10) major surface; (d) said die (28) including amain body defining at least the entry side of the slit, and said landportion (60) being so connected to said main body as to be capable offlexing relative thereto in said normal direction but to resist flexingin the direction of article advance in said path; (e) said land portionbeing formed integrally with said main body; and (f) said load-exertingmeans exerting said load directly on the land portion.
 5. A coating headas defined in claim 4, characterized in that said land portion (60) iscantilevered with respect to said main body (28).
 6. A coating head asdefined in claim 4, characterized in that said land portion (60) isflexibly connected to said main body (28) on two opposed sides of saidland portion.
 7. A coating head as defined in claim 4, characterized inthat said load-exerting means (48) comprises at least one piston (50)movable in said normal direction and means connected to said piston (50)for transmitting said load directly to said land portion (60), saidlast-mentioned means being interengageable with said main die body forpermitting but limiting the extent of motion of the piston (50) and landportion (60) relative to said main body in said normal direction.
 8. Acoating head as defined in claim 7, characterized in that said landportion (60) has a second surface (60 a) opposed to said land surface(30 a), said transmitting means includes a chock (74) attached to saidone piston (50), a rod (82) for load-transmitting engagement with saidsecond surface of said land portion (60), and a projection (78) carriedby said chock (74), and said main die body includes a socket (80) withinwhich said projection (78) is received, said projection and socket beingpositioned and dimensioned to permit a limited extent of motion of saidprojection (78) within said recess in said normal direction.
 9. Acoating head as defined in claim 7, characterized in that saidtransmitting means comprises means for transmitting a force from saidone piston (50) to said main die body (28) for moving said die relativeto said supporting means in said normal direction.
 10. A coating linefor continuously coating a major surface of a strip article (10) whilethe article is advancing longitudinally along a defined path, includingmeans for defining a path and direction of continuous longitudinaladvance of a strip article (10) having a major surface to be coated; anda coating head (20) including a die (28) defining an elongated slit(34), with an entry side and an exit side, for depositing a layer ofliquid coating material on a facing major surface of a strip article(10) advancing along the path, and having a land portion (60) at theslit exit side and means for supplying liquid coating material to theslit; characterized by: (a) said land portion (60) having an extendedland surface (30 a) at the exit side of slit (34); (b) means forsupporting the die (28) with the slit (34) and land surface (30 a)facing the path and the slit (34) extending transversely of the pathsuch that during coating operation a major surface of a strip article(10) advancing in the path past the slit (34) drags a layer of coatingmaterial from the slit, said supporting means permitting movement of thedie (28) relative thereto in a direction normal to the path and to theslit (34); (c) means for continuously exerting a load on at least theland portion (60) of the die during operation as aforesaid such that thelayer of coating material deposited on the last-mentioned article (10)major surface is pressed between the land surface (30 a) and thelast-mentioned article (10) major surface to maintain the layer at apredetermined constant thickness while the layer alone holds the die(28) entirely away from contact with the last-mentioned article (10)major surface; (d) said die (28) including a main body defining at leastthe entry side of the slit, and said land portion (60) being soconnected to said main body as to be capable of flexing relative theretoin said normal direction but to resist flexing in the direction ofarticle advance in said path; (e) said land portion being formedintegrally with said main body; and (f) said load-exerting meansexerting said load directly on the land portion.
 11. A coating line asdefined in claim 10, for continuous coating of an elongated striparticle (10) having two opposed major surfaces to be coated,characterized in that said path includes a rectilinear portion in whichsaid opposed surfaces are substantially planar, wherein saiddie-supporting means supports said die (28) at said rectilinear portionof said path such that during a coating operation said slit (34) facesone of the opposed major surfaces of a strip article advancing alongsaid path; and further including a second coating head (22), disposed atsaid rectilinear path portion in opposed relation to saidfirst-mentioned coating head, for depositing a layer of liquid coatingmaterial on the other of the opposed major surfaces of thelast-mentioned strip article (10).
 12. A coating line as defined inclaim 10, for continuous coating of an elongated strip article (10)having two opposed major surfaces of which only one is to be coated,further characterized by means (562) for supporting said strip at alocation in said path, said strip-supporting means (562) engaging thesurface of said strip opposite said one surface at said location suchthat said one surface is exposed for coating at said location, andwherein said die-supporting means supports said die at said locationsuch that during a coating operation said slit (34) faces said onesurface of a strip article (10) advancing along said path, fordepositing a layer of liquid coating material thereon.